Positioning of mobile devices

ABSTRACT

A base station transmits, in a repetitive first sequence of transmission frames of a wireless channel, first positioning reference signals. The base station transmits, in a repetitive second sequence of transmission frames of the wireless channel, second positioning reference signals. The first positioning reference signals and the second positioning reference signals each facilitate determining a time of arrival of signals communicated on the wireless channel.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation application claiming the benefit ofU.S. patent application Ser. No. 16/323,709, filed Feb. 6, 2019, whichis a national stage application of International Application No.PCT/EP2016/069130, filed Aug. 11, 2016, the disclosures of which areincorporated herein by reference in their entireties.

TECHNICAL FIELD

Various examples relate to positioning of mobile devices. In particular,various examples relate to positioning of mobile devices based oncommunication of positioning reference signals via a wireless channelcomprising transmission frames.

BACKGROUND

Positioning techniques for mobile devices are applied in various fieldsof technology. Sometimes, positioning techniques are combined withwireless communication. In this context, a particular technique is theObserved Time Difference Of Arrival (OTDOA). Here, downlink (DL)positioning reference signals are transmitted by a plurality of basestations and received by a mobile device. The mobile device can thendetermine the time-difference of arrival (TDOA), sometimes also referredto as Reference Signal Time Difference (RSTD). The TDOA can thuscorrespond to the observed time difference between the positioningreference signals received from a target base station and the referencebase station. In some examples, it is possible that the mobile devicedetermines the TDOA for two or more base stations: this then typicallyinvolves three or more base stations, because one base station is usedas the reference.

Then, based on the TDOA, location information for the mobile device canbe calculated. The location information may be indicative of theposition of the mobile device. For determining the location information,the predefined locations of the base stations involved and/or predefinedtime offsets between the involved base stations can be considered. Insome examples, a location server may determine the location informationbased on triangulation. OTDOA techniques are described in the ThirdGeneration Partnership Project (3GPP) Technical Specification (TS)36.211 V13.2.0 (2016-06), chapter 6.10.4., TS 36.355 V13.1.0 (2016-03)chapter 6.5.1., as well as TS 36.455 V13.1.0 (2016-03) chapter 8.2.5.

However, such OTDOA positioning techniques according to referenceimplementations face certain drawbacks and restrictions. For example,the accuracy of such positioning techniques may be limited. For example,the energy consumption for receiving and processing the positioningreference signals can be significant.

SUMMARY

Therefore, a need exists for advanced positioning techniques for mobiledevices. In particular, a need exists for such techniques which overcomeor mitigate at least some of the above identified drawbacks andrestrictions.

According to an example, a base station includes an interface. Theinterface is configured to communicate on a wireless channel. The basestation further includes at least one processor. The at least oneprocessor is configured to transmit first positioning reference signals.The first positioning reference signals are transmitted in a repetitivefirst sequence of transmission frames of the wireless channel. The basestation is further configured to transmit second positioning referencesignals. The second positioning reference signals are transmitted in arepetitive second sequence of transmission frames of the wirelesschannel. The second sequence is at least partly different from the firstsequence. The first positioning reference signals and the secondpositioning reference signals each facilitate determining a time ofarrival of signals communicated on the wireless channel.

According to an example, a device includes an interface. The interfaceis configured to communicate on a wireless channel. The device furtherincludes at least one processor. The at least one processor isconfigured to select between a repetitive first sequence of transmissionframes of the wireless channel and a repetitive second sequence oftransmission frames of the wireless channel. The at least one processoris further configured to selectively receive first positioning referencesignals in the first sequence or second positioning reference signals inthe second sequence depending on said selecting. The at least oneprocessor is further configured to determine a time of arrival ofsignals communicated on the wireless channel selectively based on thefirst positioning reference signals or the second positioning referencesignals depending on said selecting.

According to an example, a network node includes an interface. Theinterface is configured to communicate with at least one of a pluralityof base stations and a device. The network node further includes atleast one processor. The at least one processor is configured tocommunicate a control message to at least one of a given one of theplurality of base stations and the device. The at least one controlmessage is indicative of a repetitive first sequence of transmissionframes of a wireless channel in which the given base station is totransmit first positioning reference signals to the device. The at leastone control message is further indicative of a repetitive secondsequence of transmission frames of the wireless channel in which thegiven base station is to transmit second positioning reference signalsto the device. The first positioning reference signals and the secondpositioning reference signals each facilitate determining of a time ofarrival of signals communicated on the wireless channel.

According to an example, a method includes transmitting firstpositioning reference signals in a repetitive first sequence oftransmission frames of a wireless channel. The method further includestransmitting second positioning reference signals in a repetitive secondsequence of transmission frames of the wireless channel. The secondsequence is at least partly different from the first sequence. The firstpositioning reference signals and the second positioning referencesignals each facilitate determining a time of arrival of signalscommunicated on the wireless channel.

According to an example, a computer program product includes programcode. The program code can be executed by at least one processor.Executing the program code by the at least one processor causes the atleast one processor to perform a method. The method includestransmitting first positioning reference signals in a repetitive firstsequence of transmission frames of a wireless channel. The methodfurther includes transmitting second positioning reference signals in arepetitive second sequence of transmission frames of the wirelesschannel. The second sequence is at least partly different from the firstsequence. The first positioning reference signals and the secondpositioning reference signals each facilitate determining a time ofarrival of signals communicated on the wireless channel.

According to an example, a computer program includes program code. Theprogram code can be executed by at least one processor. Executing theprogram code by the at least one processor causes the at least oneprocessor to perform a method. The method includes transmitting firstpositioning reference signals in a repetitive first sequence oftransmission frames of a wireless channel. The method further includestransmitting second positioning reference signals in a repetitive secondsequence of transmission frames of the wireless channel. The secondsequence is at least partly different from the first sequence. The firstpositioning reference signals and the second positioning referencesignals each facilitate determining a time of arrival of signalscommunicated on the wireless channel.

According to an example, a method includes selecting between arepetitive first sequence of transmission frames of a wireless channeland a repetitive second sequence of transmission frames of the wirelesschannel. The method further includes selectively receiving firstpositioning reference signals in the first sequence or secondpositioning reference signals in the second sequence, depending on saidselecting. The method further includes determining a time of arrival ofsignals communicated on the wireless channel depending on saidselecting. Said determining is selectively based on the firstpositioning reference signals or the second positioning referencesignals.

According to an example, a computer program product includes programcode. The program code can be executed by at least one processor.Executing the program code by the at least one processor causes the atleast one processor to perform a method. The method includes selectingbetween a repetitive first sequence of transmission frames of a wirelesschannel and a repetitive second sequence of transmission frames of thewireless channel. The method further includes selectively receivingfirst positioning reference signals in the first sequence or secondpositioning reference signals in the second sequence, depending on saidselecting. The method further includes determining a time of arrival ofsignals communicated on the wireless channel depending on saidselecting. Said determining is selectively based on the firstpositioning reference signals or the second positioning referencesignals.

According to an example, a computer program includes program code. Theprogram code can be executed by at least one processor. Executing theprogram code by the at least one processor causes the at least oneprocessor to perform a method. The method includes selecting between arepetitive first sequence of transmission frames of a wireless channeland a repetitive second sequence of transmission frames of the wirelesschannel. The method further includes selectively receiving firstpositioning reference signals in the first sequence or secondpositioning reference signals in the second sequence, depending on saidselecting. The method further includes determining a time of arrival ofsignals communicated on the wireless channel depending on saidselecting. Said determining is selectively based on the firstpositioning reference signals or the second positioning referencesignals.

According to an example, a method includes communicating at least onecontrol message to at least one of a base station and a device. The atleast one control message is indicative of a repetitive first sequenceof transmission frames of a wireless channel in which the base stationis to transmit first positioning reference signals to the device. The atleast one control message is further indicative of a repetitive secondsequence of transmission frames of the wireless channel in which thebase station is to transmit second positioning reference signals to thedevice. The first positioning reference signals and the secondpositioning reference signals each facilitate determining a time ofarrival of signals communicated on the wireless channel.

According to an example, a computer program product includes programcode. The program code can be executed by at least one processor.Executing the program code by the at least one processor causes the atleast one processor to perform a method. The method includescommunicating at least one control message to at least one of a basestation and a device. The at least one control message is indicative ofa repetitive first sequence of transmission frames of a wireless channelin which the base station is to transmit first positioning referencesignals to the device. The at least one control message is furtherindicative of a repetitive second sequence of transmission frames of thewireless channel in which the base station is to transmit secondpositioning reference signals to the device. The first positioningreference signals and the second positioning reference signals eachfacilitate determining a time of arrival of signals communicated on thewireless channel.

According to an example, a computer program includes program code. Theprogram code can be executed by at least one processor. Executing theprogram code by the at least one processor causes the at least oneprocessor to perform a method. The method includes communicating atleast one control message to at least one of a base station and adevice. The at least one control message is indicative of a repetitivefirst sequence of transmission frames of a wireless channel in which thebase station is to transmit first positioning reference signals to thedevice. The at least one control message is further indicative of arepetitive second sequence of transmission frames of the wirelesschannel in which the base station is to transmit second positioningreference signals to the device. The first positioning reference signalsand the second positioning reference signals each facilitate determininga time of arrival of signals communicated on the wireless channel.

It is to be understood that the features mentioned above and those yetto be explained below may be used not only in the respectivecombinations indicated, but also in other combinations or in isolationwithout departing from the scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically illustrates communication of DL positioningreference signals from a plurality of base stations of a cellularnetwork to a mobile device according to various embodiments.

FIG. 2 schematically illustrates a resource mapping of a subframe of awireless channel comprising a plurality of resources allocated fortransmission of DL positioning reference signals according to variousembodiments.

FIG. 3 schematically illustrates a sequence of subframes of the wirelesschannel comprising a plurality of resources allocated for transmissionof DL positioning reference signals, wherein the sequences is repeatedaccording to a timing schedule according to various embodiments.

FIG. 4 schematically illustrates the architecture of a cellular networkconfigured for positioning of a mobile device according to variousembodiments.

FIG. 5 schematically illustrates a server network node of the cellularnetwork according to various embodiments.

FIG. 6 schematically illustrates a base station of the cellular networkaccording to various embodiments.

FIG. 7 schematically illustrates a mobile device of the cellular networkaccording to various embodiments.

FIG. 8 is a flowchart of a method according to various embodiments.

FIG. 9A schematically illustrates determining a time-difference ofarrival according to various embodiments.

FIG. 9B schematically illustrates determining a time-difference ofarrival according to various embodiments.

FIG. 10 schematically illustrates a sequence of subframes of thewireless channel comprising a plurality of resources allocated fortransmission of DL positioning reference signals, wherein the sequencesis repeated according to a timing schedule according to variousembodiments.

FIG. 11 schematically illustrates a resource mapping of a subframe of awireless channel comprising a plurality of resources allocated fortransmission of DL positioning reference signals according to variousembodiments.

FIG. 12 schematically illustrates a sequence of subframes of thewireless channel comprising a plurality of resources allocated fortransmission of DL positioning reference signals, wherein the sequencesis repeated according to a timing schedule according to variousembodiments.

FIG. 13 schematically illustrates a resource mapping of a subframe of awireless channel comprising a plurality of resources allocated fortransmission of DL positioning reference signals according to variousembodiments.

FIG. 14 schematically illustrates a resource mapping of a subframe of awireless channel comprising a plurality of resources allocated fortransmission of DL positioning reference signals according to variousembodiments.

FIG. 15 schematically illustrates a resource mapping of a subframe of awireless channel comprising a plurality of resources allocated fortransmission of DL positioning reference signals according to variousembodiments.

FIG. 16 schematically illustrates a time-difference of arrival betweentransmission and reception.

FIG. 17 schematically illustrates a resource mapping of a subframe of awireless channel comprising a plurality of resources allocated fortransmission of DL positioning reference signals according to variousembodiments.

FIG. 18 is a flowchart of a method according to various embodiments.

FIG. 19 is a flowchart of a method according to various embodiments.

FIG. 20 is a flowchart of a method according to various embodiments.

DETAILED DESCRIPTION OF EMBODIMENTS

In the following, embodiments of the invention will be described indetail with reference to the accompanying drawings. It is to beunderstood that the following description of embodiments is not to betaken in a limiting sense. The scope of the invention is not intended tobe limited by the embodiments described hereinafter or by the drawings,which are taken to be illustrative only.

The drawings are to be regarded as being schematic representations andelements illustrated in the drawings are not necessarily shown to scale.Rather, the various elements are represented such that their functionand general purpose become apparent to a person skilled in the art. Anyconnection or coupling between functional blocks, devices, components,or other physical or functional units shown in the drawings or describedherein may also be implemented by an indirect connection or coupling. Acoupling between components may also be established over a wirelessconnection. Functional blocks may be implemented in hardware, firmware,software, or a combination thereof.

Hereinafter, positioning techniques for mobile devices are described.The positioning techniques rely on the communication of positioningreference signals. In some examples, DL positioning reference signalsare transmitted by one or more base stations (BSs) and received by amobile device. While hereinafter the various examples are primarilydescribed in the context of DL positioning reference signals, generally,such techniques may also be applied to uplink (UL) positioning referencesignals.

The positioning techniques generally enable to track the position of themobile device over the course of time. For this, location dataindicative of the position of the mobile device may be determined. Basedon the location data of the mobile device, position-dependent servicescan be implemented. Examples include geo-messaging, geo-tracking, etc.

In some examples, the positioning techniques described herein may beapplied in the Internet of Things (IoT) framework. For example, this maycorrespond to the 3GPP Enhanced Machine-type Communication (eMTC) or the3GPP Narrowband Internet of Things (NB-IoT) technology: These examplesare described in 3GPP RP-161321 “New work item proposal on furtherenhanced MTC”, Ericsson, RAN #72, and RP-161324 “New work item proposal:enhancements of NB-IOT”, Vodafone, Huawei, HiSilicon, Ericsson,Qualcomm, RAN #72, respectively. Such techniques in the IoT frameworktypically aim at creating low-cost mobile devices that are powerefficient and can operate in extended coverage, e.g., such as insidebasements.

FIG. 1 illustrates aspects with respect to positioning techniquesaccording to various examples. In particular, FIG. 1 illustrates aspectswith respect to positioning techniques which rely on communication of DLpositioning reference signals 150.

FIG. 1 illustrates the architecture of a cellular network 100 accordingto some examples implementations. In particular, the cellular network100 according to the example of FIG. 1 implements the 3GPP LTEarchitecture. According to 3GPP LTE, a wireless channel is definedaccording to the evolved UMTS Terrestrial Radio Access (EUTRAN). Suchillustration in the 3GPP LTE framework is for exemplary purposes only.Similar techniques can be readily applied to various kinds of3GPP-specified architectures, such as Global Systems for MobileCommunications (GSM), Wideband Code Division Multiplex (WCDMA), GeneralPacket Radio Service (GPRS), Enhanced Data Rates for GSM Evolution(EDGE), Enhanced GPRS (EGPRS), Universal Mobile TelecommunicationsSystem (UMTS), and High Speed Packet Access (HSPA), and correspondingarchitectures of associated cellular networks. In particular, suchtechniques may be applied in 3GPP NB-IoT or eMTC systems and 3GPP NewRadio (NR) positioning. Furthermore, respective techniques may bereadily applied to various kinds of non-3GPP-specified architectures,such as Bluetooth, satellite communication, IEEE 802.11x Wi-Fitechnology, etc.

In FIG. 1, a mobile device 130 (labeled UE in FIG. 1) can receive DLpositioning reference signals 150 transmitted by each one of a pluralityof BSs 101-103. In the 3GPP LTE architecture, the BSs 101-103 areimplemented as evolved Node B's (eNBs). The positioning referencesignals 150 transmitted by different BSs 101-103 may be orthogonal withrespect to each other, e.g., in time-domain, frequency-domain, and/orcode-domain. This mitigates interference.

To facilitate positioning of the mobile device 130, the mobile device130 is typically time-synchronized with one or more of the BSs 101-103.E.g., the BSs 101-13 can be time-synchronized with one another; theserving BS 101-103 can be time-synchronized with the mobile device 130.Optionally, the BSs 101-103 are also time-synchronized with respect toeach other.

The mobile device 130 may be one of the following: a smartphone; acellular phone; a table; a notebook; a computer; a smart TV; a MTCdevice; an eMTC device; an IoT device; an NB-IoT device; etc.

FIG. 1 illustrates aspects with respect to the accuracy of determiningthe location of the mobile device 130. Typically, the accuracy ofdetermining the location of the mobile device 130 depends on theaccuracy of the measured positioning reference signals 150. For example,in FIG. 1, the determination of the time of arrival (TOA) 111 of the DLpositioning reference signals 150 transmitted by the BS 101 has anaccuracy of ΔT1; the determination of the TOA 112 of the DL positioningreference signals 150 transmitted by the BS 102 has an accuracy of ΔT2;and the determination of the TOA 113 of the DL positioning referencesignals 150 transmitted by the BS 103 has an accuracy of ΔT3. Typically,the accuracy of the TOA 111-113 measurements depends on the quality ofthe measured DL positioning reference signal and a bandwidth of the DLpositioning reference signal.

Positioning reference signals may generally correspond to well-definedsymbols transmitted via the wireless channel. The positioning referencesignals may be encoded according to predefined rules. The positioningreference signals may have a well-defined amplitude and/or symbol value.Based on such well-defined properties of the positioning referencesignals, it is possible to determine the TOA of the positioningreference signals. Various examples of positioning reference signals areconceivable. For example, in some examples, the positioning referencesignals may be encoded based on a certain sequence code. In someexamples, the sequence code may have a dependency on the time-frequencyposition of the particular resource used for transmission of thepositioning reference signal 150 via the wireless channel. In someexamples, the sequence code may have a dependency on an identity of thetransmitting BS, e.g., a cell identifier (cell ID). Thereby, thepositioning reference signals 150 may be indicative of the respectiveBSs. In some examples, the sequence code may have a dependency on thetransmission frame which includes the resource allocated fortransmission of the respective positioning reference signal 150: e.g.,this may result in positioning reference signals 150 communicated indifferent transmission frames to be encoded differently. Thereby, thepositioning reference signals may be indicative of the respectivetransmission frames. In some examples, the positioning reference signalsmay be scheduled specifically for a given mobile device 130. Differentmobile devices may be associated with different positioning referencesignals at different positioning occasions.

In some examples, the positioning reference signals employed accordingto the various examples described herein may employ the sequence codeaccording to 3GPP TS 36.211 V13.2.0 (2016-06), 6.10.4.1. In someexamples, the positioning reference signals are employed according tothe various examples described herein may employ the sequence codeaccording to 3GPP TS 36.211 V13.2.0 (2016-06), 6.10.10.1. In someexamples, the positioning reference signals are employed according tothe various examples described herein may employ the sequence codeaccording to 3GPP TS 36.211 V13.2.0 (2016-06), 6.11.2.1. In someexamples, the positioning reference signals are employed according tothe various examples described herein may employ the sequence codeaccording to 3GPP TS 36.211 V13.2.0 (2016-06), 6.11.1.1.

FIG. 2 illustrates aspects with respect to a resource mapping 301 of thewireless channel. FIG. 2 illustrates a resource mapping 301 used fortransmission of DL positioning reference signals 150 from a given BS101-103 to the mobile device 130.

The resource mapping 301 includes a plurality of time-frequencyresources 223. The various resources 223 can be orthogonal with respectto each other. In an example, a resource 223 may relate to a symbolencoded by a Orthogonal Frequency Division Multiplexing (OFDM)subcarrier. Sometimes, a resource 223 may be referred to as a resourceelement. Each resource 223 may include a cyclic prefix.

The resource mapping 301 further defines some of the resources 223 to beallocated for transmission of the DL positioning reference signals 150(in FIG. 2, the respective resources 223 are illustrated with the dashedfilling). Other resources 223 are not allocated for transmission of theDL positioning reference signals 150: such resources 223 may beallocated for transmission of control data, payload data, otherreference signals, etc. In some examples, it is also possible thatresources 223 in the vicinity of positioning reference signals 150 donot carry data to mitigate interference. For example, other resources223 may be used by other BSs for transmission of DL positioningreference signals 150.

The position of the respective resources 223 allocated for communicationof a positioning reference signal 150 may be defined with respect to asubframe 202. The subframe 202 is a particular implementation of thetransmission frame of the wireless channel. In other examples, theposition of the respective resource 223 allocated to communication of apositioning reference signal 150 may, alternatively or additionally, bedefined with respect to a frame comprising a plurality of subframes 202and/or with respect to the time slot being part of a subframe. In anexample implementation, the duration of the subframe 202 may be 1millisecond. The subframe 202 may include two time slots, each of 0.5milliseconds duration. The frame may include a plurality of subframes202, e.g., a count of ten subframes 202.

In the example of FIG. 2, the position of the respective resource 223allocated to the communication of the positioning reference signal 150is, furthermore, defined with respect to a resource block 212. Theresource block 212 includes a plurality of resources 223. Typically, thebandwidth of the wireless channel includes a plurality of resourceblocks 212, e.g., two resource blocks, ten resource blocks, fiftyresource blocks, or even hundred resource blocks (in FIG. 2, for sake ofsimplicity, only the single resource block 212 is illustrated).

To mitigate inter-BS interference, it is possible that the particularresources 223 allocated for communication of the positioning referencesignals 150 are varied from BS 101-103 to BS 101-103. Thus, differentBSs 101-103 may employ different resource mappings (in FIG. 2 only asingle resource mapping 301 is shown for simplicity). In one example,each resource mapping 101-103 including resources 223 allocated fortransmission of the positioning reference signals 150 may be uniquelyallocated to a BS 101-103. For example, the particular resources 223allocated for communication of the positioning reference signals 150 maydepend on a unique identity associated with the transmitting BS 101-103,e.g., the cell ID.

To further reduce the inter-BS interference, certain BSs 101-103 may beconfigured to alternatingly mute transmission of the positioningreference signals 150 in a time-division multiplexing (TDM) manner.Thus, such techniques enable time-division multiplexing and/orfrequency-division (FDM) multiplexing. Alternatively or additionally, itwould also be possible to employ code-division multiplexing (CDM)between the plurality of BSs 101-103 transmitting the positioningreference signals. Here, scrambling code can be employed.

To mitigate intra-BS interference and/or inter-BS interference, it ispossible that a particular subframe 202 including resources 223allocated for transmission of the positioning reference signals 150 is aprotected subframe 202. For example, the protected subframe 202 may notinclude resources 223 allocated for transmission of payload data.

Payload data may be data originating from a higher layer of thetransmission protocol stack. For example, payload data may be dataoriginating from the application layer according to the OSI model of thetransmission protocol stack. Sometimes, payload data is also referred toas user data.

Typically, a higher accuracy may be achieved for determining theposition of the mobile device 130 if a larger count of positioningreference signals 150 is communicated from each participating BS 101-103to the mobile device 130. This is why a plurality of resources 223 areallocated for transmission of the positioning reference signals 150 persubframe 202. For example, the count of resources 223 allocated fortransmission of the positioning reference signals 150 with respect tothe total count of resources 223 in the subframe 202 may define atime-frequency density of the positioning reference signals 150. Thetime-frequency density may be defined with respect to a resource block212 and/or may be defined with respect to the system bandwidth of thewireless channel. Typically, a higher time-frequency density of thepositioning reference signals 150 results in a higher accuracy fordetermining the position of the mobile device 130.

In FIG. 2, a frequency offset 280 between simultaneously communicatedpositioning reference signals 150 is illustrated. Often, a smallerfrequency offset 280 will result in a higher time-frequency density ofthe positioning reference signals 150.

FIG. 3 schematically illustrates aspects with respect to a repetitivetiming schedule 250. The repetitive timing schedule 250 is used fortransmission of DL positioning reference signals 150 from a given BS101-103 to the mobile device 130. Other BSs 101-103 may use the same ordifferent repetitive timing schedule 250. Properties of the repetitivetiming schedule 250 may be configured by the network 100 using controlsignaling, e.g., Radio Resource Control (RRC) signaling and/orNon-Access Stratum (NAS) in the example of 3GPP LTE systems.Alternatively or additionally, properties of the timing schedule 250 maybe signaled explicitly or implicitly using OTDOA parameters. Forexample, the LTE positioning protocol (LPP) as specified in 3GPP TS36.355 may be used to signal the timing schedule 250. Generally, theOTDOA parameters and/or the timing schedule 250 may be communicatedbetween a server such as a location server and the terminal and/orbetween the server and the BSs 101-103.

According to the repetitive timing schedule 250, a sequence 211 ofsubframes 202 is repeatedly transmitted. The sequence 211 includes aplurality of subframes 202 adjacent in time-domain to each other: thus,the sequence is contiguous. Each one of the subframes 202 of thesequence 211 includes at least one positioning reference signal 150 (inFIG. 3, the subframes 202 of the sequence 211 are illustrated with thedark filling). For example, there may be no subframes 202 within thesequence 211 which do not include at least one positioning referencesignal 150.

Each subframe 202 of the sequence 211 includes one or more resources 223being allocated for transmission of positioning reference signals 150.For example, in the scenario of FIG. 3, each one of the four subframes202 of the sequence 211 may be configured according to the resourcemapping 301 is illustrated in FIG. 2.

In the example of FIG. 3, a first repetition 251 of the sequence 211 anda second repetition 252 of the sequence 211 are illustrated. There maybe more than two repetitions 251, 252. E.g., the sequence 211 may berepeated infinitely.

For example, the sequence 211 may be repeatedly communicated at a givenrepetition rate. In some examples, the repetition rate may be periodic.In FIG. 3, a periodicity 255 with which the sequence 211 is repeated isillustrated.

In FIGS. 2 and 3, a bandwidth 216 used for transmission of thepositioning reference signals 150 is illustrated. In the example ofFIGS. 2 and 3, the bandwidth 216 used for the transmission of thepositioning reference signals 150 equals the entire system bandwidth ofthe wireless channel. In other examples, the bandwidth 216 may coverless than the entire system bandwidth. For example, according toreference implementations of a 3GPP LTE 20 MHz system, the bandwidth 216may be. Hence, in some examples, resources 223 of the resource mapping301 may be allocated for transmission of the positioning referencesignals 150 across the entire band width of the wireless channel or asubfraction thereof; in some examples of the techniques describedherein, it is possible that the bandwidth 216 used for transmission ofthe positioning reference signals 150 is smaller than the entirebandwidth of the wireless channel.

If the bandwidth 216 used for transmission of the positioning referencesignals 150 is smaller than the entire bandwidth of the wirelesschannel, it is possible to have different arrangements of the frequencyband of the positioning reference signals 150 within the frequency bandof the wireless channel. In some examples, the frequency band of thepositioning reference signals 150 may be centered within the frequencyband of the wireless channel. In some examples, the frequency band ofthe positioning reference signals 150 may be arranged adjacent to anupper edge or a lower edge of the frequency band of the wirelesschannel. The frequency band may be defined by upper and lower limitsand/or the center point and the frequency bandwidth.

Various techniques described herein are based on the finding that anaccuracy of the positioning of the mobile device tends to be lower ifthe bandwidth 216 is restricted. For example, in the 3GPP LTEtechnology, the sampling rate of a symbol is dependent upon thebandwidth of the wireless channel. For example, the sampling rate for asystem bandwidth of 20 MHz is 30.72 MHz: this is twice the bandwidth ofa 10 MHz system bandwidth where the sampling rate is 15.36 MHz. A highersampling rate typically result in a finer measure of the TOA and hence amore accurate determination of the distance between the respective BS101-103 and the mobile device 130. Therefore, the accuracy is dependenton the bandwidth. For example, if the positioning reference signals 150are transmitted using a bandwidth 216 of 1.4 MHz, an accuracy indetermining the location of the mobile device 130 according to referenceimplementations amounts to ±150 meters. For example, if the positioningreference signals 150 are transmitted using a bandwidth 216 of 10 MHz,an accuracy in determining the location of the mobile device 130according to reference implementations amounts to ±50 meters.

Various techniques described herein are based on the finding that forwireless channels designed for IoT applications, the systembandwidth—and with it the bandwidth 216 for transmission of thepositioning reference signals 150—is typically limited. For example,according to 3GPP NB-IoT, the system bandwidth is limited to a singleresource block 212 and thus amounts to 180 kHz. For example, accordingto 3GPP eMTC, the system bandwidth is limited to 6 resource blocks 212and thus amounts 1.4 MHz. Various examples described herein enableincreased accuracy when determining the location of a mobile device inbandwidth-limited wireless channels such as 3GPP NB-IoT and 3GPP eMTC.

FIG. 4 illustrates aspects with respect to the cellular network 100. Inparticular, FIG. 4 illustrates aspects of an architecture of thecellular network 100 for positioning the mobile device 130. Asillustrated in FIG. 4, the wireless channel 170 facilitatescommunication between each one of the BSs 101-103 and the mobile device130.

In FIG. 4, a network node 120 of the cellular network 100 which isimplemented by a server is shown. The server 120 may perform varioustasks with respect to positioning of the mobile device 130.

A first task that may be assigned to the server 120 may correspond toscheduling of the communication of the positioning reference signals150. Here, the server 120 may implement the resource mappings specifyingthe resources 223 allocated for transmission of the positioningreference signals 150 at each one of the BSs 101-103. Different BSs101-103 may thus be associated with different resource mappings: thus,different BSs 101-103 may employ different resources 223 fortransmission of the positioning reference signals 150.

A second task that may be assigned to the server 120 may correspond toimplementing the timing schedule for repeated transmission of thesequence 211 of subframes 202 which include the positioning referencesignals 150 at each one of the BSs 101-103. Different BSs 101-103 mayuse different timing schedules, including different repetition rates 255and/or lengths of the sequences 211.

A third task that may be assigned to the server 120 may correspond todetermining location information based on positioning informationprovided by the mobile device 130. Here, it is possible that thepositioning information provided by the mobile device 130 is indicativeof a TDOA of the positioning reference signals 150 received from eachone of the BSs 101-103 with respect to the positioning reference signals150 received from a reference BS 101-103. Then, the server 120 canperform triangulation taking into account the positioning information,as well as predefined positions of the BSs 101-103, e.g., defined withrespect to the reference BS. Based on the triangulation, the location ofthe mobile device 130 with respect to the BSs 101-103 may be determined.Then, the location information can be indicative of the determinedposition of the mobile device 130. This third task may also be executedby a separate location server (not shown in FIG. 4).

FIG. 5 schematically illustrates aspects with respect to the server 120.The server 120 includes a processor 1201, an interface 1202, and amemory 1203. It is possible that the memory 1203 stores program codethat may be executed by the processor 1201. Executing the program codecan cause the processor 1201 to perform various tasks with respect topositioning of the mobile device 130. Such tasks may include thescheduling of the communication of the positioning reference signals150, determining timing schedules for repetitive transmission ofsequences of subframes including positioning reference signals 150, aswell as the determining of the location information based on positioninginformation indicative of the TDOAs provided by the mobile device 130.The processor 1201 may exchange messages with the BSs 101-103, as wellas with the mobile device 130 via the interface 1202.

FIG. 6 schematically illustrates aspects with respect to the BSs101-103. The BSs 101-103 each include a processor 1101, an interface1102, and a memory 1103. It is possible that the memory 1103 storesprogram code that may be executed by the processor 1101. Executing theprogram code can cause the processor 1101 to perform various tasks withrespect to positioning of the mobile device 130. Such tasks may includecommunicating the positioning reference signals 150 in accordance withthe respective resource mapping which includes resources 223 allocatedfor transmission of the positioning reference signals 150. Such tasksmay further include communicating the positioning reference signals 150in the sequence 211 of subframes 202. The timing of the sequence 211 ofsubframes 202 may be defined by the respective timing schedule. Suchtasks may further include the encoding of the positioning referencesignals 150 according to a certain sequence code. The interface 1102 maybe configured to transmit DL signals and receive UL signals via thewireless channel 170.

FIG. 7 schematically illustrates aspects with respect to the mobiledevice 130. The mobile device 130 includes a processor 1301, aninterface 1302, and a memory 1303. It is possible that the memory 1303stores program code that may be executed by the processor 1301.Executing the program code can cause the processor 1301 to performvarious tasks with respect to positioning of the mobile device 130. Suchtasks include communicating the positioning reference signals 150 inaccordance with the resource mapping which includes resources 223allocated for transmission of the positioning reference signals 150. Themobile device may receive positioning reference signals 150 fromdifferent BSs 101-101; different BSs 101-103 may use different resourcemappings. Such tasks may further include communicating the positioningreference signals 150 in the sequence 211 of subframes 202. The timingof the sequence 211 of subframes 202 may be defined by the timingschedule. Again, different BSs 101-103 may use different timingschedules. Such tasks may further include decoding of the positioningreference signals 150 according to a certain sequence code. Theinterface 1302 may be configured to receive DL signals and transmit ULsignals via the wireless channel 170.

FIG. 8 is a flowchart of a method according to various examples. Themethod according to FIG. 8 illustrates various aspects with respect topositioning of the mobile device 130.

First, in block 5001, the reference TOA is determined. For this, themobile device 130 may receive one or more positioning reference signals150 from a reference BS 101-103. Then, the mobile device 130 maydetermine the time-of-flight between the reference BS 101-103transmitting the one or more positioning reference signals 150 and themobile device 130 receiving the one or more positioning referencesignals 150. From this, the TOA can be derived. Typically, determiningthe reference TOA is a task which requires significant computationalefforts.

Next, in block 5002, the TOA is determined for a given BS 101-103different from the reference BS 101-103. Again, the mobile device 130may receive one or more positioning reference signals 150 from the givenBS 101-103. Then, the mobile device 130 may determine the time-of-flightbetween the given BS 101-103 transmitting the one or more positioningreference signals 150 and the mobile device the receiving of the one ormore positioning reference signals 150. Again, determining the TOA inblock 5002 is a task which requires significant computational efforts.

In block 5003 it is checked whether positioning reference signals 150are available from a further BS 101-103 different from the reference BS101-103, as well as different from any BS 101-103 for which previouslypositioning reference signals in block 5002 have been received and forwhich previously in block 5002 the TOA has been determined.

If said checking in block 5003 yields that positioning reference signals150 are available from a further BS 101-103, block 5002 is re-executedanew for said further BS 101-103.

Once the TOA has been determined for all available BSs 101-103 bymultiple iterations of block 5002, the method commences in block 5004.In block 5004, the TDOAs are determined. For this, the reference TOAdetermined in block 5002 may be combined or, generally, set intorelationship, with each one of the TOAs for the further BSs 101-103determined in block 5002.

Typically, the determining of the TDOAs in block 5004 is a task which isexecuted by the mobile device 130, e.g., by the processor 1301. However,in other example implementations, it would also be possible that themobile device 130 provides positioning information which is indicativeof the TOAs determined in blocks 5001, 5002 to the server 120. Then,block 5004 is a task which can be executed by the server 120, e.g., bythe processor 1201, or a location server.

Finally, in block 5005, the location information is determined. Thelocation information specifies the position of the mobile device 130,e.g., in an absolute reference system such as latitude and longitude.The location information in block 5005 is typically determined based ontriangulation of the TDOAs determined in block 5004.

Typically, the determining of the location information in block 5005 isa task which is executed by the server 120, e.g., by the processor 1201,or a location server. However, in other example implementations, itwould also be possible that the mobile device 130 determines thelocation information locally.

For example, blocks 5001-5005 may be re-executed for each subframe 202including the positioning reference signals 150. In other examples,blocks 5001-5004 may be re-executed for each repetition 251, 252 of thesequence including multiple subframes 202, each one of the multiplesubframes 202 including positioning reference signals 150 from one ormore of the BSs 101-103. Thereby, the location information can beup-to-date and, e.g., the position of the mobile device 130 can betracked.

FIG. 9A illustrates aspects with respect to determining of TOAs 111-116of positioning reference signals communicated on the wireless channel170 by different BSs 101-106. In detail, FIG. 9A illustrates an examplein which the TOAs 111-116 are determined by the mobile device 130.

In FIG. 9A, an antenna 1302A is coupled with the interface 1302. In theexample of FIG. 9A, the interface 1302 implements an analog front end.

The analogue signals received via the wireless channel 170 by theinterface 1302 are digitized and transformed into frequency domain. Forthis, a Fast Fourier Transform (FFT) is applied. The symbolscorresponding to the different resources 223 can then be individuallypost-processed. For example, as illustrated in FIG. 9A, it is possibleto implement different processing pipelines for the positioningreference signals 151-156 received from the different BSs 101-106. Whilein the example of FIG. 9A positioning reference signals 151-156 arereceived from a count of six BSs 101-106, in other examples, positioningreference signals may be received from a smaller or larger count of BSs.

Each of the pipelines includes a channel estimator. Following channelestimation, each pipeline converts the respective channel estimate intothe time domain using an inverted FFT operation. Then, the TOA 911-916is determined within each pipeline.

Typically, the channel estimation and the inverted FFT requiresignificant computational efforts. For example, processing resources maybe required to execute the inverted FFT. Additionally, typically,positioning reference signals 151-156 need to be buffered in the memory1303. Typically, each received reference signal 151-156 is representedby a floating-point number. Because there may be multiple positioningreference signals 151-156 for each BS 101-106 per subframe 202, this mayresult in a significant usage of memory resources.

FIG. 9B illustrates aspects with respect to determining of TOAs 111, 112of positioning reference signals communicated on the wireless channel170 by different BSs 101, 102. In detail, FIG. 9B illustrates an examplein which the TOAs 111, 112 are determined by the mobile device 130. FIG.9B generally corresponds to FIG. 9A.

In the example of FIG. 9B, the channel estimators of each pipelineimplement combination of a plurality of positioning reference signals150 received from the respective BS 101, 102. For example, a value canbe determined which is indicative of a plurality of positioningreference signals 150 based on a combination of at least some of thepositioning reference signals 150 received in the respective sequence ofsubframes 202. E.g., the symbols of the various positioning referencesignals 150 may be summed. Then, the respective TOA 111, 112 can bedetermined based on the value.

In the example of FIG. 9B, the UE performs least square (LS) channelestimation to obtain the coarse channel weight. The obtained channelweight can be filtered in time and/or frequency domain to obtain finerresults (filter in FIG. 9B).

Such techniques relax memory requirements. This is because it is notrequired to store each received positioning reference signals 150.Rather, it is only required to store the combined value.

Such techniques further increase the signal-to-noise ration. This isbecause multiple positioning reference signals 150 are combined beforedetermining the TOA. This facilitates coverage enhancement.

FIG. 10 schematically illustrates aspects with respect to a repetitivetiming schedule 250. The repetitive timing schedule 250 is used fortransmission of DL positioning reference signals 551, 552 from a givenBS 101-106 to the mobile device 130. Other BSs 101-106 may use the sameor different repetitive timing schedule 250. FIG. 10 illustrates aspectswith respect to multiple repetitive sequences 501, 502, each one of themultiple repetitive sequences 501, 502 comprising a plurality ofsubframes 202.

The repetitive sequence 501 includes subframes 202 including positioningreference signals 551. The repetitive sequence 502 includes subframes202 including positioning reference signals 552. The positioningreference signals 551, as well as the positioning reference signals 552both originate from one and the same given BS 101-106.

The positioning reference signals 551 facilitate determining the TOA ofsignals communicated between said given BS and the mobile device 130;likewise, the positioning reference signals 552 facilitate determiningthe TOA of signals communicated between said given BS and the mobiledevice 130. As such, both, the positioning reference signals 551, aswell as the positioning reference signals 552 are conclusive in thesense that the TOA for the given BS can be determined solely based onthe respective positioning reference signals 551, 552. Based on the TOA,the TDOA can be determined.

Generally, it is possible that the mobile device 130 is configured toreceive, both, the positioning reference signals 551, as well as thepositioning reference signals 552. In other examples, it is alsopossible that the mobile device 130 is configured to receive either thepositioning reference signals 551 or the positioning reference signals552. For example, the mobile device 130 can be configured to selectbetween the repetitive sequence 501 and the repetitive sequence 502.Then, depending on said selecting, the mobile device 130 may selectivelyreceive the positioning reference signals 551 in the sequence 501—or mayrather receive the positioning reference signals 552 in the sequence502. The TOA can then be determined selectively based on the positioningreference signals 551 or based on the positioning reference signals 552.

To distinguish between the positioning reference signals 551 and thepositioning reference signals 552, TDM and/or FDM and/or CDM techniquesmay be employed. Here, for CDM techniques, scrambling code may besuperimposed on sequence code which is used to encode the positioningreference signals 551, 552. The scrambling code may be specific for thepositioning reference signals 551 or the positioning reference signals552.

The positioning reference signals 552 can, in some examples, supplementthe positioning reference signals 551. By supplementing the positioningreference signals 551 using the positioning reference signals 552,extended coverage can be provided. In particular, by supplementing thepositioning reference signals 551 by the positioning reference signals552, additional data based on which the positioning of the mobile device130 can be implemented is provided. This increases the accuracy ofdetermining the position of the mobile device 130.

In particular, it is possible to provide coverage for receivingpositioning reference signals 151, 152 for MTC mobile devices operatingin coverage enhanced mode, e.g., Mode B operation in eMTC. This isachieved by enabling the MTC mobile device to perform additional TOAmeasurements based on positioning reference signals 551, 552 transmittedby BSs 101-106 that are further away. Thereby, the available positioningdata is increased such that the positioning accuracy may be improved.

In one example, the mobile device 130 can be configured to selectbetween the sequences 501, 502 based on the receive power of signalscommunicated on the wireless channel 170. For example, the mobile device130 can be configured to select between the sequences 501, 502 based onthe receive power of the respective positioning reference signals 551,552. In one example, if the receive power of the positioning referencesignals 551 is below a threshold, the mobile device 130 can select thesequence 502 and thus receive the positioning reference signals 552. Asillustrated in FIG. 10, the sequence 502 includes a larger count ofsubframes 202 if compared to the sequence 501. Therefore, in someexamples, it is possible to receive a larger count of positioningreference signals 552 per repetition 251, 252 if compared to the countof positioning reference signals 551 per repetition 251, 252. Thisfacilitates coverage enhancement.

It is, alternatively or additionally, possible that the mobile device130 is configured to select between the sequence 501 of subframes 202and the sequence 502 of subframes 202 based on the receive bandwidth ofits interface 1302. For example, it is possible that the mobile device130 implemented according to MTC requirements and/or according to NB-IOTrequirements has an interface 1302 of limited complexity. In particular,it would be possible that the received bandwidth of the interface 1302is limited if compared to legacy 3GPP LTE EUTRAN. For example, accordingto 3GPP NB-IoT, the system bandwidth and the bandwidth of the interface1302 may be limited to a single resource block 212 and thus amount to180 kHz. For example, according to 3GPP eMTC, the system bandwidth andthe bandwidth of the interface 1302 may be limited to 6 resource blocks212 and thus amounts 1.4 MHz. This facilitates reception of positioningreference signals 551, 552 having bandwidth 216 tailored to the receivebandwidth of the interface 1302.

In one example, the mobile device 130 can be configured to determine avalue indicative of a combination of the received positioning referencesignals 551, 552 and, then, determine the time of arrival based on saidvalue. Then, the TOA can be determined based on said value (cf. FIG.9B).

By such techniques of combining—e.g., summing up—of the receivedpositioning reference signals 551, 552, the mobile device 130 canaccumulate the energy of the received positioning reference signals 551,552 throughout the respective sequence 501, 502 of subframes 202.Thereby, the quality—e.g., measured in terms of signal-to-noise ratio—ofthe received positioning reference signals 551, 552 can be increased.Thereby, coverage enhancement can be achieved.

To facilitate the coverage enhancement and interoperability with IOTapplications, it is possible that the time-frequency density of thepositioning reference signals 552 in the subframes 202 of the sequence502 is larger than the time-frequency density of the positioningreference signals 551 in the subframes 202 of the sequence 501. It is,in particular, possible that the time-frequency density of thepositioning reference signals 552 per resource block 212 is larger thanthe time-frequency density of the positioning reference signals 551 perresource block 212. It is, in particular, possible that the count ofpositioning reference signals 552 per resource block 212 is larger thanthe count of positioning reference signals 551 per resource block 212.

For example, different BSs may use different time-frequency densities ofthe positioning reference signals.

Generally, the count of positioning reference signals 551 in a subframe202 of the sequence 501 may be different from the count of positioningreference signals 552 in a transmission frame 202 of the sequence 502.The count of positioning reference signals 551, 552 per subframe 202 maydepend on the time-frequency density of the positioning referencesignals 551, 552, the count of positioning reference signals 551, 552per resource block 212, and the bandwidth 216. For example, it may bepossible that the positioning reference signals 551 are transmitted in afrequency band that has a larger bandwidth 216 than the frequency bandused for transmission of the positioning reference signals 552. I.e.,different frequency bands 215 may be used for the transmission of thepositioning reference signals 551, 552. For example, the bandwidth 216of the frequency band used for transmission of the positioning referencesignals 552 may be tailored for the needs of the reduced bandwidth eMTCor NB-IOT technologies.

As illustrated in FIG. 10, the repetition rate 255-2 of the sequence 502may be smaller than the repetition rate 255-1 of the sequence 501. Sucha scenario facilitates transmission of payload data by limiting theoverhead due to a transmission of the positioning reference signals 552in the subframes 202 of the sequence 502. In particular, in a scenariousing protected subframes 202 for the transmission of the positioningreference signals 552, lowering the repetition rate 255-2 if compared tothe repetition rate 255-1 may be advantageous in terms of overhead. Atthe same time, such a low repetition rate 255-2 may attribute for thefinding that eMTC or NB-IoT devices at least in some scenarios may havea comparably low mobility. Then, a sampling frequency with which thelocation information for the respective mobile device 130 is determinedcan be comparably low; this, again, facilitates reduction of therepetition rate 255-2.

In the example of FIG. 10, the sequences 501, 502 are partiallyoverlapping in time domain for the repetition 251. In other examples, itwould be possible that the sequences 501, 502 do not overlap in timedomain, i.e., are offset in time-domain for all repetitions 251, 252;thereby, TDM can be implemented in order to avoid interference betweenthe transmission of the positioning reference signals 551 and thetransmission of the positioning reference signals 552. TDM can also beimplementing by superimposing the timing schedules 250 of the sequences501, 502 with sequence-specific muting patterns. The muting patterns maybe arranged such that the positioning reference signals 551, 552 are notsimultaneously transmitted. Thereby, interference between thepositioning reference signals 551, 552 is reduced.

In the example of FIG. 10, the length of the sequence 501 is shorterthan the length of the sequence 502. This facilitates accumulation ofsufficient positioning reference signals 552 per repetition 251, 252.This, again, facilitates coverage enhancement.

FIG. 11 illustrates a resource mapping 301 used for the transmission ofthe positioning reference signals 551 (left side of FIG. 11) and aresource mapping 302 used for the transmission of the positioningreference signals 552 (right side of FIG. 11). The positioning referencesignals 551, as well as the positioning reference signals 552 aretransmitted by a given BS 101-106 and received by the mobile device 130.

In FIG. 11, the resource mappings 301, 302 are illustrated for a givenresource block 223. However, the resource mapping 301 and/or theresource mapping 302 may also cover further resource blocks (notillustrated in FIG. 11 for simplicity

As illustrated in FIG. 11, the resource mappings 301, 302 used for thetransmission of the positioning reference signals 551, 552,respectively, differ partially from each other. Hence, it is possiblethat the positioning reference signals 551 are allocated to at leastpartially different resources 223 in a given resource block 212 ifcompared to the positioning reference signals 552. TDM and FDM arefacilitated. Interference between transmission of the positioningreference signals 551, 552 is mitigated.

In the example of FIG. 11, the resource mapping 302 of the positioningreference signals 552 implements a higher time-frequency density of thepositioning reference signals 552 within the resource block 212 ifcompared to the resource mapping 301 of the positioning referencesignals 551. In particular, in the example of FIG. 11, thetime-frequency density of the positioning reference signals 552 is twiceas large as the time-frequency density of the positioning referencesignals 551.

Further, the frequency offset 280 between simultaneously transmittedpositioning reference signals 551, 552 is decreased for the resourcemapping 302 of the positioning reference signals 552 if compared to theresource mapping 301 of the positioning reference signals 551. Indetail, for each resource 223 of the resource mapping 301 allocated fortransmission of a positioning reference signal 551, the resource mapping302 of the positioning reference signals 552 includes an additionalresource 223 additionally allocated for transmission of a respectivepositioning reference signal 552. Two positioning reference signals 552are allocated to resources 223 directly adjacent to each other in theresource mapping 302. For example, the resource mappings 301, 302 may bestatic. For example, a wrap around with respect to the boundaries of theresource block 212 may be applied. For example, in FIG. 11 an additionalpositioning reference signal 552 is aligned directly adjacent infrequency to the positioning references signals 551. For the positioningreference signal 551 in the fifth depicted OFDM symbol and the firstsubcarrier, there is no respective resource 223 available: wrap aroundwith respect to the boundary of the resource block 212 can be applied anthe additional positioning reference signal 552 is transmitted on theresource element of the fifth OFDM symbol and the twelfth subcarrier.

In the scenario of FIG. 11, due to the increased count of positioningreference signals 551, 552 per resource block 212 and/or per subframe202, it is possible that the count of BSs 101-106 transmittingpositioning reference signal in the same resource block 212 is limited.For example, according to reference implementations, the count of sixBSs 101-106 could transmit positioning reference signals in the sameresource block 212 (cf. FIG. 9A). For example, according to the exampleof FIG. 11, the count of BSs which transmit positioning referencesignals in resource block 212 may be limited to three.

Such a reduced number of BSs transmitting positioning reference signalsin the same resource block facilitates unique allocation the resourcemappings 301, 302 to the given BS 101-106 transmitting the positioningreference signals 551, 552. Hence, other BSs 101-106 may use differentresource mappings for the transmission of positioning reference signalsduring the resource block 212. This mitigates inter-cell interference.

In one example, it would be possible that the resources 223 of theresource mapping 301 allocated for transmission of the positioningreference signals 551 are varied as a function of repetitions 251, 252of the sequence 501, e.g., in a cyclic manner. Alternatively oradditionally, it would be possible that the resources 223 of theresource mapping 302 allocated for transmission of the positioningreference signals 552 are varied as a function of repetitions 251, 252of the sequence 502, e.g., in a cyclic manner. Thereby, it may bepossible to achieve additional redundancy and mitigate interference.

In the example of FIG. 11, some resources 223 are allocated fortransmission of, both, the positioning reference signals 551, as well asfor transmission of the positioning reference signals 552. To avoidinterference, CDM can be employed. Then, the positioning referencesignals 551 differ from the positioning reference signals 552. In otherexamples, it would also be possible that the positioning referencesignals 551 of the shared resources implement the positioning referencesignals 552. Then, the positioning reference signals 551 do not differfrom the positioning reference signals 552.

FIG. 12 schematically illustrates aspects with respect to a repetitivetiming schedule 250. The repetitive timing schedule 250 is used fortransmission of DL positioning reference signals 551, 552 from a givenBS 101-106 to the mobile device 130. Other BSs 101-106 may use the sameor different repetitive timing schedule 250. FIG. 12 illustrates aspectswith respect to multiple repetitive sequences 501, 502, each one of themultiple repetitive sequences 501, 502 comprising a plurality ofsubframes 202. FIG. 12 generally corresponds to FIG. 10. However, in theexample of FIG. 12, the sequences 501, 502 are overlapping for eachrepetition 251, 252. As such, the subframes 202 of the sequence 501 forma subset of the subframes 202 of the sequence 502.

It is possible that the positioning reference signals 551 differ or donot differ from the positioning reference signals 552. In one example,it is possible that the positioning reference signals 151 are encodedbased on the same sequence code as the positioning reference signals152. The sequence code may have a dependency on the resource 223 usedfor transmission of the respective positioning reference signal 551,552. In one example, it is possible the resource mapping 301 definesresources 223 for transmission of the positioning reference signals 551which are also defined by the resource mapping 302 for transmission ofthe positioning reference signals 552 (cf. FIG. 11). Then, if thesequence code is shared, the respective positioning reference signals551, 552 are the same. In such a scenario, the positioning referencesignals 551 may form a subset of the positioning reference signals 552.Here, the positioning reference signal 551, 552 may be reused in theoverlap region of the sequences 501, 502 for both the sequences 501,502. This reduced overhead.

E.g., a mobile device 130 selecting the sequence 501 would stopreceiving the positioning reference signals 551 at the end of a givenrepetition 251, 252 of the sequence 501. A mobile device 130 selectingthe sequence 502 would continue receiving the positioning referencesignals 552 beyond the end of the given repetition 251, 252 of thesequence 501 and until the end of the sequence 502: further positioningreference signals 552 can be accumulated.

FIG. 13 illustrates aspects with respect to the resource mappings 301,302 of the positioning reference signals 551, 552 associated with thesequences 501, 502. In particular, the resource mapping 301, 302 may beapplied to a timing schedule 250 according to the example of FIG. 12.

In the example of FIG. 13, the positioning reference signals 551 form asubset of the positioning reference signals 552 within a given subframe202. The resources 223 allocated for transmission of the positioningreference signals 551 are re-used for transmission of the positioningreference signals 552 as well. There are additional resources 223 solelyallocated for transmission of the positioning reference signals 552.

FIG. 14 illustrates aspects with respect to resource allocation fortransmission of positioning reference signals 551, 552 by a plurality ofBSs 101-103. In the example of FIG. 14, the frequency bandwidth 216 usedfor transmission of the positioning reference signals 552 by each one ofthe BSs 101-103 is smaller than the system bandwidth 450 of the wirelesschannel. Hence, the positioning reference signals occupy a subset of allavailable resource blocks 212 in the bandwidth 450 of the wirelesschannel. Because in some examples, the positioning reference signals areemployed for positioning of MTC or NB-IoT mobile devices 130 which haveinterfaces 1302 operating at a smaller bandwidth, by restricting thebandwidth 216 accordingly, overhead can be reduced.

FIG. 14 illustrates examples with respect to transmission of positioningreference signals 551, 552 by a plurality of BSs 101-103. Variousexamples have been explained with respect to the positioning referencesignals 551, 552 all originating from the given BS. Such concepts may beapplied in various scenarios to multiple BSs 101-103 each transmittingpositioning reference signals 551, 552 in at least partially differentsequences 501, 502 of a repetitive timing schedule 250. Different BSs101-103 may use at least partially different timing schedules 250 and/orleast partially resource mappings 301, 302.

For sake of simplicity, hereinafter, various techniques are describedexemplarily with respect to the positioning reference signals 552.However, such techniques may be readily applied to the positioningreference signals 551, alternatively or additionally.

Various scenarios to avoid inter-cell interference are conceivable. Forexample, it would be possible that the resource mappings 302 of thepositioning reference signals 552 are arranged such that BSs 101-103having an even cell ID occupy a certain set of resources 223 and BSshaving an odd cell ID occupy a set of orthogonal resources 223. Here,one and the same resource blocks 212 can be shared among different BSs101-103 (not shown in FIG. 14).

In a further example, orthogonality can be achieved by having theresource mappings 302 of BSs 101-103 having an even cell ID occupyingdifferent subframes 202 than BSs 101-103 having an odd cell ID (notshown in FIG. 14). For example, a muting pattern can be superimposed onthe timing schedule 250 of the repetitions 251, 252 of the sequences 502associated with the different BSs 101-102. The muting pattern can thenbe BS-specific, i.e., each BS 101-103 may have a muting pattern that isuniquely associated with the respective BS 101-103. This corresponds toa TDM approach of avoiding interference.

As illustrated in FIG. 14, in a further example, the frequency bands 216used for transmission of the positioning reference signals 552 bydifferent BSs 101-103 may be non-overlapping. For example, the resourceblock 212 that is used by a given BS 101-103 for transmission of thepositioning reference signals 552 may be a function of the cell IDassociated with the BS 101-103. A mobile device 130 can then tune inbetween the different frequency bands including the resource blocks 212associated with a different BSs 101-103.

In general, such an approach can be extended beyond odd and even cellidentities. In one example implementations, cell_ID mod x=0 occupies oneset of resources and cell_ID mod X=1 occupies another set of resources,where cell_ID is the cell identity of a given BS.

Such concepts may be helpful where the time-frequency density of thepositioning reference signals 552 is comparably high such that it, e.g.,occupies all resources or a large fraction of all resources 223 of thegiven resource block 212 to improve coverage.

In the example of FIG. 14, frequency hopping may be employed for thefrequency bands associated with the various BSs 101-103. For example,the particular resource blocks 212 associated with a given BS 101-103may be altered as a function of the repetition 251, 252 of therespective sequence 502 of subframes 202 including the positioningreference signals 552. The frequency hop pattern may be configurable.Such techniques are described in the international patent applicationPCT/EP2016/067812 entitled “Frequency Hop Based Positioning Measurement”the respective disclosure of which is incorporated herein in itsentirety by cross-reference.

The frequency hop pattern may implement a cyclic shift of the resourceblocks 212 associated with the various BSs 101-103. This is indicated bythe curved arrows in FIG. 14. Frequency hopping may provide resilienceagainst frequency-select a fading. This may help to improve the accuracyof the positioning of the mobile device 130 by allowing measurements ofthe time of arrival to be performed across a wider effective bandwidth.

Beside concepts of avoiding inter-cell interference between multiple BSs101-103 transmitting the positioning reference signals 552 which arebased on FDM and/or TDM as explained above, alternatively oradditionally, concepts of avoiding inter-cell interference based on CDMcan be employed. For example, scrambling code can be considered in thesequence code for determining the positioning reference signals 552transmitted by different BSs 101-103.

FIG. 15 illustrates aspects with respect to resource mappings 301, 302employed for transmission of positioning reference signals 551, 552. Thepositioning reference signals 551, as well as the positioning referencesignals 552 are transmitted by a given BS 101-106 and received by themobile device 130.

Also in the scenario of FIG. 15, the resource mapping 302 of thepositioning reference signals 552 occupies a comparably small bandwidth216-2 if compared to the system bandwidth 450 of the wireless channel170. The bandwidth 216-1 of the resource mapping 301 of the positioningreference signals 551 occupies the entire system bandwidth 450.Therefore, the bandwidth 216-1 is larger than the bandwidth 216-2.

As illustrated in FIG. 15, the frequency band used for transmission ofthe positioning reference signals 552 is centered within the frequencyband used for transmission of the positioning reference signals 551.I.e., the center frequency of the frequency band used for transmissionof the positioning reference signals 552 corresponds to the centerfrequency of the frequency band used for transmission of the positioningreference signals 551.

For example, for a system bandwidth 450 amounting to 10 MHz, it ispossible that the bandwidth 216-1 equals 10 MHz while the bandwidth216-2 is restricted to 1.4 MHz. Here, to enable a mobile device 130 touse, both, the positioning reference signals 551, as well as thepositioning reference signals 552 for positioning purposes, typically,the starting resource block 212 of the positioning reference signals 551is signaled to the mobile device 130. The starting resource block 212 isrequired in order to determine the signal sequence applied to thepositioning reference signals 551. For example, it is possible that theterminal is signaled the offset 455 relative to the first resource block212 of the positioning reference signals 552 of the starting resourceblock 212 of the positioning reference signals 551.

The sequence code used for the positioning reference signals 551 in agiven resource block 212 may be a function of the particular resourceblock 212 to which the positioning reference signal 551 is applied.Alternatively or additionally, the sequence code used for a givenpositioning reference signal 551 can be a function of the differencebetween the start resource block 212 PRB_y of the positioning referencesignals 551 and the resource block 212 PRB_x of the given positioningreference signal 551, i.e., the code of the given positioning referencesignals 551 in the resource block 212 PRB_x may be a function of y-x.

Similar consideration also may apply to the positioning referencesignals 552 and the respective sequence code.

FIG. 16 illustrates aspects with respect to the TDOA 850 betweenreception of positioning reference signals 552 transmitted by differentBSs 101-104. In FIG. 16, multiple resources 223 are illustrated for eachBS 101-104: each resource 223 includes a cyclic prefix 801 and an OFDMsymbol 802.

In the example of FIG. 16, transmission by the BSs 101-104 is timesynchronized. I.e., the beginning of an new resource 223 istime-synchronized between the BSs 101-104. The BSs 101-104 all havedifferent distances from the mobile device 130. Hence, the TOAs 111-114of the respective positioning reference signals 552 are all differentfor the various BS 101-104.

FIG. 16 also illustrates the TDOA 850 between the TOAs 111, 113. In thelegacy scenarios, typically, the TDOA 850 is limited, becausepositioning reference signals are not received from BSs 101-104 locatedat a large distance with respect to the terminal 130. However, as hasbeen explained above, according to various example techniques describedherein, it is possible to implement coverage enhancement. Because ofthis, it is possible to receive the positioning reference signals 552from the BS 104. The distance between the mobile device 130 and the BS104 is so large that the respective TDOA is longer than the duration ofthe cyclic prefix 801.

Because the TDOA may be longer than the duration of the cyclic prefix801, ambiguities in determining the TDOA may result. Hence, it ispossible that the positioning reference signals 552 are indicative ofthe respective subframe 202. This may be done by using sequence codewhich shows a dependency on the sequence number of the respectivesubframe 202. For example, such a dependency of the sequence code on thesequence number of the respective transmission frame 202 may be employedusing scrambling code. For example, the positioning reference signals552 may be indicative of the boundary of the respective transmissionframe 202, e.g., the last OFDM symbols adjacent to the next subframe202. By being able to associate the received positioning referencesignal 552 with a given subframe 202, it is possible to resolveambiguities.

Such techniques as explained with respect to the positioning referencesignals 552 above may be applied, alternatively or additionally, to thepositioning reference signals 551.

FIG. 17 illustrates aspects with respect to the resource mapping 302including resources 223 allocated for transmission of the positioningreference signals 552. In the example of FIG. 17, a subframe 202includes the positioning reference signals 552. However, the positioningreference signals 552 do not occupy the last three resources/symbols 223of the subframe 202. The last 3 resources/symbols 223 in the example ofFIG. 17 implement a safety margin. In particular, as illustrated in FIG.17, lower part, the TOA 111 between transmission and reception can belonger than the cyclic prefix 801. To avoid corruption of the followingsubframe 202 (illustrated in FIG. 17, upper part, right side), thesafety margin 1700 can be employed. While in the example of FIG. 17 thesafety margin 1700 has a duration of three OFDM symbols 223, in otherexamples, the safety margin 1700 may have a longer or shorter duration.

Various examples as explained above with respect to FIGS. 16 and 17 withrespect to the positioning reference signals 552 may be readily appliedto the positioning reference signals 551, alternatively or additionally.

FIG. 18 is a flowchart of a method according to various examples. Atblock 6001, first positioning reference signals are transmitted, e.g.,by a base station. The first positioning reference signals aretransmitted according to a repetitive timing schedule. The timingschedule defines a repetitive first sequence of transmission frames. Thetransmission frames of the first sequence include the first positioningreference signals.

At block 6002, second positioning reference signals are transmitted,e.g., by the same base station which transmits the first positioningreference signals in block 6001. The second positioning referencesignals are transmitted according to a further repetitive timingschedule. The further repetitive timing schedule defines a repetitivesecond sequence of transmission frames. The transmission frames of thesecond sequence include the second positioning reference signals.

It is then possible to determine the TOA based on the received firstpositioning reference signals and/or based on the received secondpositioning reference signals.

FIG. 19 is a flowchart of a method according to various examples. Atblock 6011, selection between a repetitive first sequence oftransmission frames and repetitive second sequence of transmissionframes is made. Generally, selection can be made between more than 2sequences of transmission frames.

If at block 6011 the first sequence is selected, the method commences atblock 6012. At block 6012, first positioning reference signals arereceived in the first sequence. Then, at block 6013, the TOA can bedetermined based on the first positioning reference signals received atblock 6012.

If at block 6011 and the second sequence is selected, the methodcommences at block 6014. At block 6014, second positioning referencesignals are received in the second sequence. Then, at block 6015, theTOA can be determined based on the second positioning reference signalsreceived at block 6014.

FIG. 20 is a flowchart of a method according to various examples. Atblock 6021, at least one control message is communicated to a basestation. Alternatively or additionally, the at least one control messagemay be communicated to one or more mobile devices. The control messageis indicative of a repetitive first sequence of transmission frames anda repetitive second sequence of transmission frames. The base station isto transmit first positioning reference signals in the first sequenceand second positioning reference signals and the second sequence.

Although the invention has been shown and described with respect tocertain preferred embodiments, equivalents and modifications will occurto others skilled in the art upon the reading and understanding of thespecification. The present invention includes all such equivalents andmodifications and is limited only by the scope of the appended claims.

The invention claimed is:
 1. A base station, comprising: an interfaceconfigured to communicate on a wireless channel, and at least oneprocessor configured to transmit, in a repetitive first sequence oftransmission frames of the wireless channel, first positioning referencesignals and to transmit, in a repetitive second sequence of transmissionframes of the wireless channel which is at least partly different fromthe first sequence, second positioning reference signals, wherein thefirst positioning reference signals and the second positioning referencesignals each facilitate determining a time of arrival of signalscommunicated on the wireless channel, and wherein a count of the firstpositioning reference signals in the transmission frames of the firstsequence is different from a count of the second positioning referencesignals in the transmission frames of the second sequence.
 2. The basestation of claim 1, wherein the count of the first positioning referencesignals per subframe of the transmission frames of the first sequence isdifferent from the count of the second positioning reference signals persubframe of the transmission frames of the second sequence.
 3. The basestation of claim 1, wherein the count of the first positioning referencesignals per resource block of the transmission frames of the firstsequence is different from the count of the second positioning referencesignals per resource block of the transmission frames of the secondsequence.
 4. The base station of claim 1, wherein the first positioningreference signals are encoded based on a first sequence code, whereinthe second positioning reference signals are encoded based on a secondsequence code, and wherein the first sequence code and the secondsequence code are the same.
 5. The base station of claim 1, wherein thefirst positioning reference signals are indicative of a respectivetransmission frame, and/or wherein the second positioning referencesignals are indicative of a respective transmission frame.
 6. The basestation of claim 1, wherein the first positioning reference signals donot occupy at least the last resource of each one of the respectivetransmission frames, preferably at least the last two resources, morepreferably at least the last three resources, and/or wherein the secondpositioning reference signals do not occupy at least the last resourceof each one of the respective transmission frames, preferably at leastthe last two resources, more preferably at least the last threeresources.
 7. The base station of claim 1, wherein the time-frequencydensity of the first positioning reference signals in the transmissionframes of the first sequence is different from the time-frequencydensity of the second positioning reference signals in the transmissionframes of the second sequence.
 8. The base station of claim 1, whereinthe frequency band of the first positioning reference signals isdifferent from the frequency band of the second positioning referencesignals.
 9. The base station of claim 1, wherein a repetition rate ofthe first sequence is different from a repetition rate of the secondsequence.
 10. The base station of claim 1, wherein the first sequenceand the second sequence are at least partially overlapping in time. 11.The base station of claim 1, wherein the length of the first sequence islonger than the length of the second sequence.
 12. The base station ofclaim 1, wherein the first sequence is associated with a first resourcemapping of orthogonal time-frequency resources, wherein the secondsequence is associated with a second resource mapping of orthogonaltime-frequency resources, wherein the first resource mapping and thesecond resource mapping are at least partially different from eachother.
 13. The base station of claim 12, wherein the first resourcemapping and/or the second resource mapping are uniquely allocated to thebase station.
 14. The base station of claim 12, wherein the resources ofthe first resource mapping allocated for transmission of the firstpositioning reference signals are varied as a function of repetitions ofthe first sequence, and/or wherein the resources of the second resourcemapping allocated for transmission of the second positioning referencesignals are varied as a function of repetitions of the second sequence.15. A device, comprising: an interface configured to communicate on awireless channel, and at least one processor configured to selectbetween a repetitive first sequence of transmission frames of thewireless channel and a repetitive second sequence of transmission framesof the wireless channel prior to receiving the first or second sequenceof transmission frames, to selectively receive, based on said selecting,one of: first positioning reference signals in the first sequence; orsecond positioning reference signals in the second sequence, and todetermine a time of arrival of signals communicated on the wirelesschannel selectively based on the first positioning reference signals orthe second positioning reference signals depending on said selecting.16. The device of claim 15, wherein the device is configured to selectbetween the first sequence and the second sequence based on at least oneof a receive power of signals communicated on the wireless channel and areceive bandwidth of the interface.
 17. The device of claim 15, whereinthe device is configured to determine at least one first valueindicative of the first positioning reference signals based on acombination of at least some of the first positioning reference signalsand to determine the time of arrival based on the at least one firstvalue, and/or wherein the device is configured to determine at least onesecond value indicative of the second positioning reference signalsbased on a combination of at least some of the second positioningreference signals and to determine the time of arrival based on the atleast one second value.
 18. A network node, comprising: an interfaceconfigured to communicate with at least one of a plurality of basestations and a device, at least one processor configured to communicateat least one control message to at least one of a given one of theplurality of base stations and the device, the at least one controlmessage being indicative of a repetitive first sequence of transmissionframes of a wireless channel, in which the given base station is totransmit first positioning reference signals to a device and furtherindicative of a repetitive second sequence of transmission frames of thewireless channel, in which the given base station is to transmit secondpositioning reference signals to the device, wherein the firstpositioning reference signals and the second positioning referencesignals each facilitate determining of a time of arrival of signalscommunicated on the wireless channel, and wherein a count of the firstpositioning reference signals in the transmission frames of the firstsequence is different from a count of the second positioning referencesignals in the transmission frames of the second sequence.